Run whisper.cpp whisper-server on the host, and Atlas containers reach it through host.docker.internal. Select it with STT_PROVIDER_SOURCE=whisper-cpp-localhost.

• macOS: Docker Desktop containers cannot use Metal or Core ML. A host build of whisper.cpp can.
• Small footprint: one native binary and a ggml model file, with no Python or PyTorch.
• Quantized models: q5_0 and similar quantizations reduce memory use.

Atlas publishes no speed ranking against the other STT engines. Benchmark representative audio on the deployment host.

For a container-only setup, use speaches-container-cpu or parakeet-container-gpu (NVIDIA only). The STT Provider README lists all sources.

The Homebrew whisper-cpp formula does not install whisper-server (it builds with WHISPER_BUILD_SERVER=OFF). Build from source on macOS and on Linux:

git clone https://github.com/ggml-org/whisper.cpp
cd whisper.cpp
cmake -B build
cmake --build build -j --config Release

The binary is ./build/bin/whisper-server. On Apple Silicon, the default build runs inference on the GPU through Metal. For other accelerators, add one flag to the first cmake command:

Run these commands in the whisper.cpp checkout:

# English only, 142 MiB
sh ./models/download-ggml-model.sh base.en

# Multilingual, 2.9 GiB
sh ./models/download-ggml-model.sh large-v3

# Multilingual, quantized: smaller and less memory
sh ./models/download-ggml-model.sh large-v3-q5_0

The script writes models/ggml-<model>.bin. Run the script without arguments to list the other models, for example large-v3-turbo.

# The port matches WHISPER_CPP_LOCALHOST_PORT in .env (default 63042).
./build/bin/whisper-server \
  --host 0.0.0.0 \
  --port 63042 \
  --model models/ggml-large-v3.bin \
  --inference-path /v1/audio/transcriptions \
  --convert

--inference-path serves the OpenAI-compatible /v1/audio/transcriptions route that Atlas calls. --convert converts formats other than WAV, MP3 and FLAC, for example OGG/Opus voice notes. It needs ffmpeg on the PATH.

whisper-server has no authentication. --host 0.0.0.0 makes it reachable from the local network as well as from Docker. Use the host firewall when the network is not trusted.

./start.sh --stt-provider-source whisper-cpp-localhost

If the server uses a port other than 63042, set it in .env. Atlas derives the URL http://host.docker.internal:${WHISPER_CPP_LOCALHOST_PORT:-63042}:

WHISPER_CPP_LOCALHOST_PORT=18143

curl -X POST http://localhost:63042/v1/audio/transcriptions \
  -F [email protected] \
  -F model=whisper-1
# expect JSON: {"text":"..."}

whisper.cpp ignores model and uses the loaded file.

Address already in use: start the server on another port, then set WHISPER_CPP_LOCALHOST_PORT in .env.

Slow on a Mac: check that the server log reports the Metal backend. A build without Metal runs on the CPU.

Model load runs out of memory: use a quantized or smaller model, for example large-v3-q5_0 or base.en.

• whisper.cpp upstream
• whisper-server options
• Core ML support
• ggml model files